Numerous different constructions of pipes made from non-metallic materials are known. Compared with pipes made from metallic materials such pipes have many advantages, e.g. lower weight and higher corrosion resistance. Due to the latter property, such pipes are used for the carrying of corrosive material. Such non-metallic pipes can also be laid in the ground, where metal pipes are subject to strong corrosion.
Pipes made entirely from plastic materials are known and the corresponding characteristics of these plastics can be advantageously utilized. They have a low weight and, in most cases, an adequate strength, but are relatively expensive. Thus, efforts have been made to reduce the costs of such pipes without impairing the characteristics of the plastics used. Such a pipe is disclosed in EP 0 151 930. The wall of this pipe is formed from several layers built up from plastic and inorganic materials. The pipe of that patent essentially comprises a cement mortar core layer, which is surrounded by a reinforcing layer both on the inner and outer wall sides. The two reinforcing layers comprise a plastic material, e.g. a polyester, which is reinforced by means of fibres, e.g. glass fibres. Such pipes have advantages compared with purely plastic pipes in that they are less expensive than purely plastic pipes, have the same corrosion characteristics as purely plastics pipes, and have a lower weight than metal pipes.
In order that such pipes can be assembled with standard connecting or joining elements, information is given in the above-referenced industrial property right as to how the pipes can be provided with socket or sleeve connecting elements. A socket end is shaped on to one pipe end having an external diameter larger than the pipe diameter by at least twice the wall thickness. Thus, the space required for laying the same is very large and, consequently, is not cost effective. Moreover, the rotating drum in which such pipes are produced, must be shaped in accordance with the socket at the drum end which also leads to additional costs.
Admittedly, the above-referenced industrial property right describes an additional pipe, in which no use is made of a socket with a larger diameter than the pipe diameter, but rather requiring a metal ring which is inserted at one drum end and connected to the pipe body. However, in this latter embodiment it is very difficult to achieve a good connection between said metal ring and the pipe body. Further, this metal ring is also exposed to corrosion, thereby negating the advantage of the nonmetallic pipe body. Thus, this type of pipe connection has not received practical acceptance.
The problem solved by the present invention is to further develop a method of the aforementioned type such that a composite or compound pipe with socket connecting elements can be produced in which said elements are also made from nonmetallic materials and do not project over the pipe body diameter, while maintaining a strength between the socket connecting elements and the pipe body that is comparable to that of the pipe body. According to the present invention this problem is solved by simultaneously constructing a composite layered pipe body wherein one pipe end is provided with a socket end having a projection and the other pipe end is provided with a spigot end having an offset, and further wherein the shaping of the pipe ends of the socket material corresponds to that of the reinforcing layer of the pipe body.
The present invention also covers an apparatus enabling the production of composite pipes with socket connecting elements in an optimum manner. According to the present invention this problem is solved in that the shaping rings required for shaping the socket connecting elements at the pipe ends are stored over at least one horizontally mounted drum in a magazine. These shaping rings are successively brought to the drum end corresponding to the construction of the composite pipe by means of handling devices, at least one of which is set up at each drum end. The shaping rings are fixed to the drum, and subsequently replaced and returned to the magazine by means of the handling devices.